The present invention relates to a phenolic resin intended especially to be employed in a sizing composition for material based on mineral wool, especially insulating products in felt or sheet form.
The manufacture of mineral wool-based products includes a first stage of manufacture of the wool itself, especially by the known technique of centrifugal drawing in which the molten mineral material is converted into filaments, and a stage of forming in which the filaments are drawn and entrained towards a receiving member by a gas stream at a high speed and temperature, to form a mat thereon. To ensure the cohesion of the mat, a so-called sizing composition, which contains a heat-curable resin is sprayed onto the wool during its travel towards the receiving member. The mat thus treated is next subjected to an oven heat treatment to polycondense (cure) the resin and obtain a product exhibiting desired properties, such as dimensional stability, tensile strength, thickness regain after compression and homogeneous colour.
The sizing compositions are generally sprayed onto the mineral wool and are prepared in the form of an aqueous composition (solution, dispersion). This composition is in general prepared shortly before spraying, on the actual production site, by addition of the usual constituents: a curing catalyst such as ammonium sulphate, urea and possible adjuvants such as lubricating mineral oils as antidust agent, aqueous ammonia, silanes as adhesiveness promoter and silicone as water-repellent.
The sprayability of such compositions is determined by the dilutability of the resin in water, which is generally defined as follows: the water-dilutability of a resin in the form of aqueous composition (resole) is the volume of deionized water which, at a given temperature, can be added to the unit volume of this composition before causing the formation of a permanent turbidity. The water dilutability of a resin suitable for being employed in a sprayable sizing composition is advantageously of the order of at least 1000% at 20xc2x0 C., that is to say that 10 ml of resin can be diluted with 10xc3x9710 ml of water or more, without the mixture becoming turbid.
It is furthermore desirable that the resin should be stable in storage to allow use at the last moment: the dilutability must therefore remain high for as long a period as possible. A resin will advantageously have a water dilutability at 20xc2x0 C. equal to or higher than 1000% for at least 8 days.
The heat-curable resin employed is generally a phenolic resole obtained by condensation of phenol and of formaldehyde, or equivalents, in the presence of a basic catalyst. To satisfy the requirement of a high water dilutability the degree of condensation of the monomers is limited, to avoid the formation of long, not very hydrophilic, molecular chains, which reduce the dilutability.
In this respect it is customary to terminate the condensation reaction at a degree of progress when the molecular chains are not very long, by neutralizing the reaction mixture to a pH of the order of 7 to 8 with a strong acid such as sulphuric acid, which has the effect of deactivating the basic catalysis. The resole then contains a certain proportion of starting materials, phenol and formaldehyde, which have not reacted.
Furthermore, to limit the risks of atmospheric pollution during the processing of the sizing composition, it is desirable that the composition employed should be as free as possible from volatile organic compounds such as the unconverted starting materials, free phenol and formaldehyde, or from other materials capable of being formed during the condensation of the monomers, and that it should generate as few polluting by-products as possible during the spraying onto the filaments at elevated temperature and/or when passing in the oven. The content of monomers, in particular free phenol and, above all, volatile phenolic derivatives, could in theory be reduced by increasing the duration and the degree of condensation of the resins, but there would then be a loss in the dilutability of the resin.
The problem which underlies the invention consists in satisfying as well as possible these two contradictory requirements.
To reduce the free phenol content in the resin it is generally proposed to prepare the phenolic resole by reacting phenol with formaldehyde in a form aldehyde/phenol molar ratio higher than 1, which promotes the consumption of the phenol, and then to add urea, which reacts with excess formaldehyde. Resins formed of formaldehyde/phenol and urea/formaldehyde condensates are thus obtained. The resin may be neutralized before or after the addition of urea, which has the additional effect of shifting the equilibrium of the reversible reaction between urea and formaldehyde towards the formation of the condensation product. It is generally preferred to neutralize the resin at a pH close to 7 to avoid the release of polluting starting materials.
Document EP-A-0 148 050 describes the preparation by this technique of resins which have a water dilutability of at least 1000% and which have a free phenol content (by weight relative to the total weight of liquid resin) lower than or equal to 0.5%, and a free formaldehyde content (by weight relative to the total weight of liquid resin) lower than or equal to 3%.
In the ideal case all the urea ought to be added to the resole at the time of the manufacture of the resin to simplify the preparation of the sizing composition on site. However, the modification of the resole by the urea can result in a partial precuring of the sizing and in difficulties in handling downstream. This is why the resole, which still contains a certain proportion of formaldehyde is modified only partially, and urea is added again to the sizing composition. These sizing compositions must nevertheless be employed fairly quickly because their storage period is relatively limited.
EP-A-0 512 908 provides a means for reducing the precuring and increasing the storage period before use of a sizing prepared from a modified resole of this type. It consists in reacting the neutralized resole with two nitrogenous reactors, namely aqueous ammonia and urea.
Other modifications of the resins, aimed at improving other properties of the sizing, are also known from the prior art.
Thus, U.S. Pat. No. 4,176,105 concerns the preparation of a binder for mineral fibres, based on a phenolic resol of improved heat resistance, capable of with-standing a heat curing operation without undergoing flameless exothermic decomposition (also known as xe2x80x9cpunkingxe2x80x9d) which is usually responsible for colour defects in mineral wool-based products. It proposes to prepare a modified phenolic prepolymer of low molecular weight in three stages consisting in combining a phenol-formaldehyde condensate of low molecular weight, consisting essentially of polyhydroxymethylphenols, with a water-soluble boron compound such as boric acid as far as an acidic pH of the order of 2, and then adjusting the pH of the mixture to a value of the order of 7 to 9 with a base such as ammonium hydroxide and, finally, adding a difunctional nitrogen compound such as urea.
U.S. Pat. No. 5,032,431 discloses the use of a water-soluble borate for improving the moisture resistance of phenolic resin-based compositions cured in alkaline medium, employed in the manufacture of glass fibre-based dark-coloured insulating materials. The borate, such as lithium, sodium or potassium metaborate, can be simply added to the alkaline phenolic resol of pH higher than 8.5 or else can be manufactured in situ by reaction of boric acid with the appropriate alkali metal hydroxide in a sufficient quantity for the pH of the composition to remain higher than 8.5.
While the resins and sizing compositions prepared in the way set out above offer quite a satisfactory compromise between the free phenol and formaldehyde content and the dilutability, it is always desirable to improve this performance. The aim of the invention is to provide a resin for sizing composition which has a very low content of polluting volatile organic compounds, not only phenol and formaldehyde, but also volatile organic derivatives such as monomethylolphenols, which is dilutable and preferably stable in storage for a period at least equal to that of the resins known at present, and which is in addition easy to prepare.
The present invention is based on the unexpected discovery that it is possible to prepare a dilutable and stable resin composition from a highly condensed phenolic resole, whose dilutability in basic medium may be relatively low, and that precipitates in general in sulphuric acid medium. The invention consequently makes it possible to prepare phenolic resins which are not highly polluting by the route consisting in pushing the condensation reaction towards products of high molecular weight, while solving the problem of processing the resin on the manufacture site.
In this respect, the first subject-matter of the invention is a resin composition based on a urea-modified phenol-formaldehyde resole which has a formaldehyde/phenol molar ratio of the order of 2 to 5, exhibiting a free formaldehyde content lower than or equal to 3% (by weight relative to the total weight of the composition), a free phenol content lower than or equal to 0.5% and a dilutability measured at 20xc2x0 C. of at least 1000%, characterized in that it contains an overcondensed resole obtained by condensation of phenol, of formaldehyde and optionally of urea in basic medium until the product has a water dilutability at pH 9 lower than or equal to 2000%, or the product of neutralization of such a resole.
The invention enables to provide stable resin compositions, having a dilutability measured at 20xc2x0 C. of at least 1000% for at least 3 weeks"" storage at 12xc2x0 C., even where they comprise the product of neutralization of the overcondensed resole.
In the present invention, the phenol-formaldehyde resole may be modified with urea in the known manner, by reaction with heating, especially as described in EP-A-0 148 050, or cold, after an optional period of rest at the ambient temperature of the product of phenol-formaldehyde condensation.
In the present description the term xe2x80x9covercondensed resolexe2x80x9d denotes a resole characterized, at the end of the condensation stage of phenol, formaldehyde and optionally urea, by a relatively high proportion of large oligomers containing at least three intercondensed nuclei, and by a high average molecular weight, for example, but without any limitation being implied, higher than or equal to 500. This resole is obtained by increasing the period and/or the temperature of reaction relative to the conventional resins, and hence the degree of condensation, so as to ensure a virtually quantitative conversion of the initial phenol while going beyond the stage of the monocondensation to monomethylolphenols. It therefore contains a very low proportion of free phenol and volatile phenolic compounds capable of polluting the atmosphere at the site of use.
The high proportion of relatively water-repellent species of high molecular weight in the resole is reflected in a relatively low dilutability of the resin.
The overcondensed nature of the resoles which can be employed according to the invention is expressed by the dilutability of the basic mixture (at pH approximately 9) at the end of reaction between phenol, formaldehyde and optionally urea, which is lower than or equal to 2000%, in the case of a reaction mixture 5 whose solids content is especially of the order of 40 to 60% by weight.
The invention advantageously employs very highly condensed resoles of dilutability lower than or equal to 1500%, or else to 1000%, especially of the order of 400 to 900%.
The invention advantageously makes it possible to reach a free phenol content lower than or equal to 0.2%, and even of 0.1% or less.
In general, an overcondensed resole has a very low dilutability, particularly lower than 500%, or even nil, when it is neutralized with sulphuric acid. A precipitation can be observed as soon as the pH reaches a value of the order of 8 to 8.5.
It may nevertheless be desirable to employ the resole in neutralized form in the resin composition, in particular to prevent the urea-formaldehyde condensates from releasing the free monomers.
In a first alternative form the invention proposes to neutralize the resole with boric acid or an equivalent borate, such as ammonium borate, sodium metaborate, sodium tetraborate, aminoalcohol polyborates . . . This is because it has been discovered by the inventors that, surprisingly, the boric acid employed as neutralizing agent for an overcondensed phenolic resol modifies the resole in such a way that its dilutability is higher in the neutralized medium thus obtained than in the medium obtained with sulphuric acid. The product of neutralization of such a resole with boric acid has in general a dilutability at 20xc2x0 C. of at least 1000%, very often of the order of 2000% or more.
Without wishing to be bound by any scientific theory whatsoever, it is assumed that with the phenol-formaldehyde condensates boric acid forms polar borate complexes which impart a strong hydrophilic character to the molecular chains, promoting the solubility in aqueous medium.
In a preferred embodiment the resin composition based on a resole neutralized with boric acid is substantially neutral, with a pH of the order of 7 to 8.
However, it may also be basic, for example with a pH of the order of 8 to 10, especially from 8.5 to 10, when the neutralization of the resole is performed with boric acid in alkaline, especially ammoniacal, solution. Surprisingly, it has been found that the highly condensed resole modified with boric acid is stable in basic medium.
Regardless of their pH, all these compositions containing a product of neutralization with boric acid have a water dilutability at 20xc2x0 C. higher than or equal to 1000% for at least 3 weeks"" storage at 12xc2x0 C.
In a second alternative form the invention proposes to neutralize the resole with sulphamic acid or an equivalent sulphamate. This is because it has also been discovered by the inventors that, surprisingly, the sulphamic acid employed as neutralizing agent for an overcondensed phenolic resol modifies the resole in such a way that its dilutability is higher in the neutralized medium thus obtained than in the medium obtained with sulphuric acid. The product of neutralization of such a resole with sulphamic acid has in general a dilutability at 20xc2x0 C. of at least 1000%, very often of the order of 2000% or more.
The resin composition based on a resole neutralized with sulphamic acid is in general substantially neutral, with a pH of the order of 7 to 8.
It has a dilutability at 20xc2x0 C. of at least 1000% for at least 3 weeks"" storage at 12xc2x0 C.
In another alternative form the resin composition contains a product of neutralization with any acid, but also contains an emulsifier such as a gum and/or an anionic surfactant, especially guar and ghatti gums, or optionally caseine.
Preferably, where a common strong acid is used, the product of neutralization of the resole is obtained in the presence of the emulsifier.
The acid employed may be chosen from any strong acids which are known per se, such as sulphuric acid, hydrochloric acid, as well as boric acid or an equivalent borate, or sulphamic acid or an equivalent suplhamate.
The composition advantageously has a pH of the order of 7 to 8, especially 7.2 to 7.6.
It is in the form of an emulsion. The quantity of emulsifier which is employed depends on its nature and is easily determined by a person skilled in the art. To give an indication, this quantity may be from 1 to 10 parts by weight of emulsifier per 100 parts by weight of solids content in the resole.
As in the preceding variants, such a composition is stable and keeps a dilutability at 20xc2x0 C. of at least 1000% after 3 weeks"" storage a 12xc2x0 C.
In another embodiment the resole is not neutralized just after its preparation. This is because, as it is sought to reach a degree of condensation which is as high as possible, in order to limit the emission of pollutants, there is no absolute need to deactivate the basic catalyst rapidly. In this embodiment the resin composition according to the invention contains an unneutralized phenol-formaldehyde-urea resole. The pH of such a composition is generally of the order of 8.5 to 10.
A particular subject-matter of the invention thus is a resin composition containing an overcondensed resole whose dilutability at pH 9 is lower than or equal to 2000%, especially of the order 1000 to 2000%, in an unneutralized form, for extemporaneous mixing with a neutralizing reactant.
This composition is stable in storage and can be employed as a premix which can be completed at the last moment on the site of use by extemporaneous mixing with the ingredients necessary for the sizing formulation.
Among these ingredients, a neutralizing reactant will be added in particular because of course, it is always desirable when the objective is to avoid pollution that the resin should be in neutralized form at the time of the application of the sizing and/or of the passage in an oven.
This neutralizing reactant may be chosen advantageously from boric acid or an equivalent borate, sulphamic acid or an equivalent sulphamate, and a system including an emulsifier and an acid, as described above.
As an alternative, the resin composition according to the invention may contain an acid-precursor neutralizing reactant acting with a delay, especially under heat activation. Thus, for example, ammonium sulphate or aluminum sulphate, added to the resin composition at ambient temperature does not modify the pH of the latter, but releases sulphuric acid at elevated temperature. The quantity of ammonium sulphate in the composition is determined so as to introduce a sufficient quantity of H2SO4 equivalents to neutralize the basic catalyst present in the resole.
In the particular case where the phenol-formaldehyde-urea resole is sprayable in the unneutralized state, especially with a dilutability at pH 9 of the order of approximately from 1000 to 2000%, or even less, but more generally approximately from 1500 to 2000%, the neutralizing reactant may be added at the spraying stage, in the form of a jet of aqueous solution or dispersion sprayed at the sizing crown ring. The use of an acid-precursor neutralizing reactant capable of acting with a delay, especially under heat activation, also lends itself to this alternative form, it being possible for the heat activation to take place, for example, when the sizing composition is applied to the hot filaments of mineral material or when the mat passes through the oven.
A subject-matter of the invention is therefore a process for manufacturing a mineral wool-based product, wherein mineral wool is produced, a sizing composition is sprayed onto the wool, the sized wool is collected as a mat, and the mat is subjected to a heat treatment, characterized in that the sizing composition comprises a resin composition including a heat activation neutralizing reactant.
Another subject-matter of the invention is a process for manufacturing a mineral wool-based product, wherein mineral wool is produced, a sizing composition is sprayed onto the wool, the sized wool is collected as a mat, and the mat is subjected to a heat treatment, characterized in that the sizing composition comprises a resin composition including an unneutralized resole and a heat activation neutralizing reactant is further sprayed onto the wool.
Another subject-matter of the invention is a process for the preparation of a resin composition such as above. This process includes a characteristic stage of overcondensation, consisting in reacting phenol, formaldehyde and optionally urea in basic medium until the product has a water dilutability at pH 9 lower than or equal to 2000%, especially 1500%, or even 1000%, followed by a neutralization stage.
The initial pH (before neutralization) of the resole obtained in basic medium is generally of the order of 8.5 to 10, especially from 9 to 9.5.
In the overcondensation stage phenol and formaldehyde are reacted in the presence of a basic catalyst, the formaldehyde/phenol ratio being of the order of 2 to 5, preferably from 2.5 to 4, especially from 2.8 to 3.6. The basic catalyst known per se, especially sodium hydroxide, potassium hydroxide, calcium hydroxide or barium hydroxide, or an amine catalyst, is in general employed in a quantity corresponding to 6 to 20 moles of OH_hydroxyl equivalents per 100 moles of initial phenol.
This reaction is advantageously conducted until a degree of conversion of phenol is obtained which is equal to or higher than 98%, preferably 99%, very particularly of the order of at least 99.3 to 99.5%.
In a first alternative form the monomers are brought into contact with a basic polymerization catalyst preferably at a temperature of approximately between 20 and 60xc2x0 C., and are taken to a reaction temperature of approximately between 50 and 80xc2x0 C., preferably approximately 70xc2x0 C., up to the desired degree of conversion. This reaction temperature is maintained advantageously for 100 to 200 minutes, preferably approximately from 130 to 160 minutes. This prolonged heating allows the overcondensation of the resin to be reached with formation of species of high molecular weight containing a higher proportion of large oligomers containing three or more intercondensed phenolic nuclei. The mixture is then cooled to a temperature of 20 to 30xc2x0 C.
In a second alternative form the monomers are brought into contact with a basic polymerization catalyst preferably at a temperature of approximately between 20 and 60xc2x0 C., and are taken to a first reaction temperature of approximately between 50 and 80xc2x0 C., preferably of approximately 70xc2x0 C., and then the temperature of the mixture is raised to a second reaction temperature of between 70 and 90xc2x0 C., preferably 85xc2x0 C., up to the desired degree of conversion. This second heating plateau is intended to produce an overcondensation of the resin with formation of high molecular weight species containing a higher proportion of large oligomers containing three or more intercondensed phenolic nuclei.
Advantageously, the reaction period at the first temperature is from 50 to 80 minutes and the reaction period at the second temperature is from 30 to 60 minutes. The mixture is then cooled to a temperature of 20 to 30xc2x0 C.
In a general manner, one or more of the condensation monomers may also be fed continuously into the reaction mixture.
The preparation of the resin composition additionally includes modifying the product of phenol-formaldehyde condensation by reacting it with urea. In a first form of modification, urea is allowed to condense with the monomers in the hot reaction mixture. The urea is advantageously introduced into the reaction mixture during the cooling stage, especially as soon as the cooling begins. It may also be added after complete cooling of the reaction mixture, optionally after a certain period of storage at ambient or lower temperature. It may further be added, preferably cold, after the neutralization stage.
The neutralization stage may take place just after the overcondensation stage (the mixture being cold), or else after a stage of storage for a specified period following the overcondensation stage. It may in particular take place just before the formulation of the sizing.
It consists in adding an acid to the reaction mixture cooled to ambient temperature in sufficient quantity to lower the pH to a value of 7 to 8. The acid is advantageously introduced in a proportion of 0.88 to 0.92 mol of acid per mole of OHxe2x88x92 hydroxyl equivalents introduced by the basic catalyst.
In the case of boric acid, the boric acid is preferably employed in aqueous solution preferably assaying for 3 to 20% by weight of boric acid. The solutions with a high boric acid assay generally contain a base, such as aqueous ammonia, intended to increase the solubility of the boric acid. The quantity of boric acid to be introduced is always calculated in order to neutralize the basic catalyst, but the final pH is then higher, of the order of 8.5 to 10.
In the case of sulphamic acid, the sulphamic acid is preferably employed in aqueous solution preferably assaying for 10 to 20% by weight of sulphamic acid or of a sulphamate. Sulphamic acid or sulphamate may also be used in the solid form to be solved into the resole.
At the end of the neutralization with boric acid, the resole is seen to have its water dilutability increased in relation to that in the initial basic medium. This advantageous effect is however not limited to neutralization of an overcondensed resole, but may be observed generally with any usual phenolic resin. If, with the latter, it is difficult to observe the increase in dilutability when treating the alkaline medium with the acid, because the initial dilutability is already high, neutralization with boric or sulphamic acid increases the stability of the resin with time. Where the resole is neutralized with one of those acids, the resin composition keeps a desired level of dilutability for a longer period of time than where the resole is neutralized with sulphuric acid.
In this respect another subject-matter of the invention is a process for improving the dilutability of a phenolic resole, especially with a water dilutability at pH 9 lower than or equal to 2000%, characterized in that it includes a stage consisting in neutralizing the resole with boric (or equivalent borate) or sulphamic acid (or equivalent sulphamate).
In another embodiment an acid and an emulsifier are added at the same time during the neutralization stage. Preferably, in the case of a common strong acid, the emulsifier is added first of all, especially in aqueous solution, and then the acid, so as to perform neutralization in the presence of the emulsifier.
In yet another embodiment the neutralization stage includes the mixing of the resole with a heat-activated neutralizing reactant, and heating the resulting mixture, it being possible for this heating to take place during the spraying on the hot glass filaments or the passage of the mat through the oven.
The dilutable and stable resin compositions according to the invention may be employed advantageously in a sizing composition for a mineral wool-based product which is not highly polluting and which additionally has a high sprayability.
Another subject-matter of the invention is a sizing composition for a mineral wool-based product, including a resin composition as described above, optionally additional urea and optionally sizing additives, the weight proportions of the resin and of the urea being preferably from 50:50 to 90:10.
In general, a typical sizing composition may include the following additives, per 100 parts by weight of solids content of resin and of urea:
Ammonia may be added into the hot resin composition, or else cold as a premix after the condensation, or even when formulating the sizing, or at plural stages in the production of the composition.